1. Field
Embodiments disclosed herein relate to a non-volatile semiconductor memory device.
2. Description of the Related Art
In recent years, as succeeding candidates of flash memories, resistance change memory devices which use variable resistance elements as memory elements are gaining attention. Meanwhile, the resistance change memory devices include, for example, a narrowly-defined resistive RAM (ReRAM) which stores a resistance value state of a transition metal oxide in a non-volatile manner using the transition metal oxide for a recording layer, and a phase change RAM (PCRAM) which utilizes resistance value information of a crystalline state (conductor) and non-crystalline state (insulator) of chalcogenide using, for example, chalcogenide for a recording layer.
Memory cells of the resistance change memory device are known to have two types of operation modes. One mode is directed to setting a high-resistance state and a low-resistance state by switching the polarity of an applied voltage, and is referred to as “bipolar type”. The other one is directed to setting a high-resistance state and a low-resistance state by controlling a voltage value and a voltage application time without switching the polarity of the applied voltage, and is referred to as “unipolar type”.
To realize a high density memory cell array in a resistance change memory device, the cell array is formed by overlaying variable resistance elements and rectifying elements such as diodes on intersection parts of bit lines and word lines. Further, by providing a three-dimensional layered alignment of this memory cell array, it is possible to realize a large capacity without increasing a cell array area.
To function the resistance change elements as memory cells of the resistance change memory, it is necessary to perform forming as an initial setting operation. This forming is performed by applying a high predetermined voltage compared to data writing to variable resistance elements, forming current paths in the variable resistance elements and setting a predetermined resistance state, for example, a low-resistance state. Data is written in the memory cells for which this forming is performed, by applying a predetermined voltage to variable resistance elements for a short time in case of a unipolar type ReRAM. As a result, the variable resistance elements change from a high-resistance state to a low-resistance state. Hereinafter, an operation of changing these variable resistance elements from a high-resistance state to a low-resistance state is referred to as a setting operation. By contrast with this, data is erased from the memory cell by applying a low predetermined voltage compared to the setting operation for a long time, to the variable resistance elements in the low-resistance state after the setting operation. By this operation, the variable resistance elements change from a low-resistance state to a high-resistance state. Hereinafter, an operation of changing these variable resistance elements from a low-resistance state to a high-resistance state is referred to as a resetting operation. The memory cell, for example, places a high-resistance state in a stable state (reset state) and, to store binary data, writes data by the setting operation of changing the reset state to the low-resistance state.
With this resistance change memory device, upon forming, setting or resetting, a consumption current increases, or error setting or error resetting occurs due to a leak current to the memory cells other than target memory cells or wiring resistance.